The invention relates to power-driven conveyors and, more particularly, to modular conveyor belts constructed of rows of belt modules hingedly interlinked end-to-end by hinge pins.
Conventional modular conveyor belts and chains are made up of modular links, or belt modules, arranged in rows. Spaced apart link ends extending from each end of the modules include aligned apertures. The link ends along one end of a row of modules are interleaved with the link ends of an adjacent row. A pivot rod, or hinge pin, journaled in the aligned apertures of the end-to-end-connected rows, connects adjacent rows together to form an endless conveyor belt capable of articulating about a drive sprocket.
In many industrial applications, articles are allowed to accumulate on a continuously moving conveyor belt before being off-loaded. Friction between the conveying surface of the moving belt and the accumulated articles causes the articles to push against each other, increasing backline pressure. Backline pressure can cause damage to the articles, excessively load the conveyor belt and its drive components, and accelerate belt wear. Rotatable elements, such as rollers, in rolling contact with the undersides of conveyed articles have been used to reduce friction and lower backline pressure.
In some conveyor belts designed for low backline pressure, cylindrical rollers are positioned on the pivot rod. But, to provide room for the rollers on the pivot rod, the belt must be designed with fewer or thinner link ends, resulting in diminished belt pull strength. Likewise, the rollers must be limited in number along a pivot rod, which introduces significant spaces between consecutive rollers and imposes a lower limit on the size of the articles that can be conveyed. The large spacing between rollers also causes more vibration and jostling of accumulating articles. Furthermore, rollers on pivot rods are typically narrow, which can cause high contact pressure on conveyed articles and on the pivot rod.
In other roller-top conveyor belts or chains, rollers are positioned on dedicated pins. In some cases, the dedicated pins are supported above the base of the belt with one or more rollers positioned on the pin between spaced end supports. This design permits a high roller density, but the rollers are generally small in diameter with a number of rows of rollers on each module. High roller density is achieved by increasing the spacing between supports, which limits the weight of the load that can be borne by the rollers without causing the pin to sag and the rollers to bind. In other cases, larger rollers supported on dedicated pins are recessed in cavities in the module""s base with only a small upper portion of the roller extending above the surface of the base. The rollers are supported on dedicated pins embedded in the walls of the cavities for strength. In these belt modules, however, the roller density is limited because the cavities reduce the pull strength of the belt. Furthermore, dirt and debris can be trapped in the cavities.
Thus, there is a need for a low backline pressure conveyor belt that has high belt pull strength and well-supported rollers arranged in a high-density pattern for handling heavy articles.
This need and others are satisfied by the invention, which provides a belt module that is formed of a base extending from a first end to a second end and transversely across its width from a first side to a second side. A first set of spaced-apart hinge elements extends from the first end of the base. A second set, offset transversely from the first set, extends from the second end of the base. Transverse apertures are formed in the hinge elements. The base has an upper deck across which are spaced a plurality of supports. A transverse opening is formed in consecutive supports. The transverse openings in the supports are aligned to accept an axle. A roller is positioned in each space between consecutive supports with the axle through an axial bore in the roller. The length of the roller bore is slightly less than the support spacing to provide formidable support for the roller. The thickness of each support, measured in the widthwise direction of the module, is much less than the space between consecutive supports to closely position the rollers across the module.
A conveyor belt can be constructed of modules according to the invention. A plurality of the modules are arranged end-to-end. The first set of hinge elements of each belt module are interleaved with the second set of hinge elements of an adjacent module. Hinge pins extend through the aligned transverse apertures of the interleaved hinge elements to form a conveyor belt with parallel rows of rollers. In a preferred version of the belt, the pitch of the belt is related to the dimension of the rollers in the pitch direction so that consecutive parallel rows of rollers are separated by a gap narrower than the dimension of the rollers in the pitch dimension. Thus, a belt made according to the invention provides low backline pressure with a high-density array of well-supported, closely-spaced rollers to support heavy articles with less vibration and jostling during accumulation and without compromising belt pull strength.